Rails - Jan 2007 - N:M find confusion

Hello!

I have an N:M mapping of tables. There are three tables involved:

constraints
  id
  name

people
  id
  first_name
  last_name

constraints_people
  constraint_id
  person_id

Here is some Ruby code that I have created in order to make the
mapping:

class Person < ActiveRecode::Base
  has_and_belongs_to_many: constraints, :class_name => "Constraint"
end

class Constraint < ActiveRecod::Base
  has_and_belongs_to_many: people, :class_name => "Person"
end

I would now like to get an array of people who have a constraint id of
e.g. 1. I don''t know how to get this result, I have now tried the
following:

sql_result = Person.find_by_sql("select person_id from
constraints_people where constraint_id = " + constraint.id.to_s)
@people = Person.find(sql_result)

But the sql_result is an assocative array and I only want the IDs. Is
it the correct way to do this with find_by_sql() or is there a better
way to get the @people filled?

Thanks!
Christoph


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Hi Cristoph.

Having defined the habtm relationship between Constraints and People,
you have several methods to navigate through them. In particular, you
have a people method in the Contraint class, so you can do

contraint.people

to get the people associated to constraint. To go the other way and find
the constraints for a given person

person.constraints

So, to get the people associated to constraint with ID 1 you just need
to find the constraint by the id and ask it for its people

Constraint.find(1).people

In general, you wouldn''t use find_by_sql but in special cases.

By the way, since you have named both tables (plural) and classes
(singular) according to Ror standars you don''t need to specify the
:class_name param in the habtm declarations, you have the default.

Regards

ceicke-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org escribi�:
> Hello!
> 
> I have an N:M mapping of tables. There are three tables involved:
> 
> constraints
>   id
>   name
> 
> people
>   id
>   first_name
>   last_name
> 
> constraints_people
>   constraint_id
>   person_id
> 
> Here is some Ruby code that I have created in order to make the
> mapping:
> 
> class Person < ActiveRecode::Base
>   has_and_belongs_to_many: constraints, :class_name =>
"Constraint"
> end
> 
> class Constraint < ActiveRecod::Base
>   has_and_belongs_to_many: people, :class_name => "Person"
> end
> 
> I would now like to get an array of people who have a constraint id of
> e.g. 1. I don''t know how to get this result, I have now tried the
> following:
> 
> sql_result = Person.find_by_sql("select person_id from
> constraints_people where constraint_id = " + constraint.id.to_s)
> @people = Person.find(sql_result)
> 
> But the sql_result is an assocative array and I only want the IDs. Is
> it the correct way to do this with find_by_sql() or is there a better
> way to get the @people filled?
> 
> Thanks!
> Christoph
> 
> 
> > 
-- 
Andr�s Cirugeda Esco
ASPgems
Email: andres at aspgems dot com

''All we have to decide is what to do with the time that is given to
us''.
Gandalf.


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ceicke-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org wrote:
> Hello!
> 
> I have an N:M mapping of tables. There are three tables involved:
> 
> constraints
>   id
>   name
> 
> people
>   id
>   first_name
>   last_name
> 
> constraints_people
>   constraint_id
>   person_id
> 
> Here is some Ruby code that I have created in order to make the
> mapping:
> 
> class Person < ActiveRecode::Base
>   has_and_belongs_to_many: constraints, :class_name =>
"Constraint"
> end
> 
> class Constraint < ActiveRecod::Base
>   has_and_belongs_to_many: people, :class_name => "Person"
> end
> 
> I would now like to get an array of people who have a constraint id of
> e.g. 1. I don''t know how to get this result, I have now tried the
> following:
> 
> sql_result = Person.find_by_sql("select person_id from
> constraints_people where constraint_id = " + constraint.id.to_s)
> @people = Person.find(sql_result)
> 
> But the sql_result is an assocative array and I only want the IDs. Is
> it the correct way to do this with find_by_sql() or is there a better
> way to get the @people filled?
All you need is

   @people = constraint.people

given that you''ve found constraint using something like

   constraint = Constraint.find(1)

-- 
We develop, watch us RoR, in numbers too big to ignore.


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Ouch.. hurts to see the beginners use find_by_sql and such. Poor
php/java developers aren''t used to the beauty of ruby =(

Read the beginners guides here: http://wiki.rubyonrails.com/rails

On Jan 23, 12:23 pm, Mark Reginald James
<m...-bzGI/hKkdgQnC9Muvcwxkw@public.gmane.org>
wrote:
> cei...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org wrote:
> > Hello!
>
> > I have an N:M mapping of tables. There are three tables involved:
>
> > constraints
> >   id
> >   name
>
> > people
> >   id
> >   first_name
> >   last_name
>
> > constraints_people
> >   constraint_id
> >   person_id
>
> > Here is some Ruby code that I have created in order to make the
> > mapping:
>
> > class Person < ActiveRecode::Base
> >   has_and_belongs_to_many: constraints, :class_name =>
"Constraint"
> > end
>
> > class Constraint < ActiveRecod::Base
> >   has_and_belongs_to_many: people, :class_name =>
"Person"
> > end
>
> > I would now like to get an array of people who have a constraint id of
> > e.g. 1. I don''t know how to get this result, I have now tried
the
> > following:
>
> > sql_result = Person.find_by_sql("select person_id from
> > constraints_people where constraint_id = " + constraint.id.to_s)
> > @people = Person.find(sql_result)
>
> > But the sql_result is an assocative array and I only want the IDs. Is
> > it the correct way to do this with find_by_sql() or is there a better
> > way to get the @people filled?All you need is
>
>    @people = constraint.people
>
> given that you''ve found constraint using something like
>
>    constraint = Constraint.find(1)
> 
> --
> We develop, watch us RoR, in numbers too big to ignore.

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